Zeolites are alumino-silicate crystalline minerals which have a microporous structure. Zeolites have an “open” structure that can accommodate a wide variety of molecules and zeolites are often referred to as “molecular sieves”. The term molecular sieve refers to a particular property of zeolite materials, i.e. their ability to selectively sort molecules based primarily on a size exclusion process. The size exclusion process is due to a highly regular pore structure of molecular dimensions of the zeolite. The maximum size of a molecular or ionic substance that can enter the pores of the zeolite is controlled by the diameters of the channels (or tunnels) within the zeolite. These channels are conventionally defined by the ring size of the aperture, where, for example, the term “8ring” refers to a closed loop that is built from 8 tetrahedrally coordinated silicon (or aluminium) atoms and 8 oxygen atoms. These rings are not always perfectly flat and symmetrical, this is due to a variety of effects, including strain induced by the bonding between units that are needed to produce the overall structure, or coordination of some of the oxygen atoms of the rings to cations within the zeolite structure. Therefore, the pore openings for all channels may not be identical.
Conjugated systems (i.e. a molecular substance of covalently bonded atoms linked to one another by alternate single and double bonds) have unique properties that give rise to strong colours. Many pigments (and dyes) make use of conjugated electron systems, such as beta-carotene's long conjugated hydrocarbon chain resulting in a strong orange colour. When an electron in a conjugated system absorbs a photon of light of a specific wavelength, the electron can be promoted to a higher energy level.
Conjugated systems form the basis of chromophores. Chromophores are light-absorbing parts of a molecule which can cause the molecular substance to be coloured. Such chromophores are often present in various organic compounds and sometimes present in polymers, which are coloured or glow in the dark. They are usually caused by conjugated ring systems with bonds such as C═O and N═N in addition to conjugated C—C bonds.
Solid state molecular packing of organic conjugated systems is one of the factors which determine their electronic and optical properties and therefore their potential use in electronic and optoelectronic devices. The solid state molecular packing of anisotropic molecular systems may lead to J-aggregation of the conjugated organic molecules.
A spectroscopic advantage of J-aggregation is the substantial line narrowing of absorption and emission spectra which is paralleled by a red-shift of absorption with respect to the corresponding molecular electronic transition. The former spectroscopic effect is related to the exciton band narrowing due to coherent coupling of molecular electronic wave functions. The latter spectroscopic effect arises from the head-to-tail coupling of the molecular transition dipole moments. The exciton band narrowing is more pronounced as the exciton is delocalised over an increasing number of molecules. The exciton delocalisation is determined by the competition between intermolecular transfer interactions and static disorder imposed by the molecular environment.
Therefore to form J-aggregates in the solid state, the molecular packing and the solid state molecular ordering of the conjugated systems needs to be specifically tailored and controlled.
The organisation of organic conjugated molecular systems into nano and sub-nanoscale scaffold structures is an appealing methodology towards the formation of tailoring such highly specific structured conjugated molecular systems.
Zeolites exhibit internal channels on the nano and sub-nanometre scale, furthermore zeolites posses a defined crystalline structure and a morphology which can be tuned between the micro and the nano scale. Zeolites have applications in a number of industrial applications such as photonics and optoelectronics, these include, but are not limited to; nonlinear optics (Cox, S D et al., Chem. Mater. 1990, 2, 609), micro-lasers (Vietze U et al, M. Phys. Rev. Lett., 1998, 81.4628), light harvesting, electroluminescent devices and charge separation.
However, fundamental problems exist as to how molecules diffuse and intercalate into the channels of zeolites, how the intercalated molecules are organised within the zeolite channels and as a consequence of their organisation, how they react within the zeolite channels and interact with each other inside these scaffold channels.
A zeolite L crystal possesses a crystalline structure and sub-nanometre one-dimensional channels making the zeolite L crystal an appealing host for the organisation of conjugated molecules (such as fluorescent dyes) by the intercalation of the conjugated molecules in the channels of the zeolite L crystal. The channels of the zeolite L crystal have an entrance diameter of 7.1 {acute over (Å)}(Angstroms, 0.1 nm, 10−1 m), a maximum cage diameter of 12.6 {acute over (Å)} and a single unit cell length of 7.5 {acute over (Å)}. Furthermore the zeolite L crystal comprise a parallel channels which are separated by a distance of 18.4 {acute over (Å)}.
Based on the one-dimensionality of the channels of the zeolite L crystal, space restrictions are more prevalent in the zeolite L crystal than in the other zeolite structures, such as zeolite X or zeolite Y. This makes the zeolite L crystal more attractive as a scaffold for packing the conjugated molecule to achieve J aggregation of the conjugated molecules.
Pyronine intercalated, and oxonine intercalated with zeolite L crystal systems (FIG. 1b and 1c) are ideal for fundamental studies of unidirectional energy transfer, and such systems are known in the art, as well as applications in highly fluorescent self assembling micro objects.
It is accepted that such intercalated chromophore molecules are individually aligned at defined angles and may not slide, or stack on top of each other, thus preventing excimer formation and J-aggregate formation. Smaller, neutral molecules that may stack on top of each other have been shown to possess excimer transitions.
Interestingly, the “end to end” alignment of conjugated chromophore molecules like pyronine and oxonine can be envisaged to result in J-aggregate type coupling. The specific teachings to achieve this phenomenon are so far unreported.
Observing and understanding such excitonic J-aggregate type coupling in one dimensional channel systems is therefore of considerable scientific and industrial interest.
Lifetime studies on pyronine intercalated zeolite L crystal have shown loading dependent multi-exponential decays indicating that the molecules of the pyronine intercalated zeolite L crystal may interact with each other or the environment. Experimental evidence is still, however, confined to bulk samples. To date, few pioneering examples of spatially resolved analysis of single microcrystals at the diffraction limit exist, but the full potential has not been reached.
U.S. Pat. No. 5,968,242 is assigned to Ciba Speciality Chemicals Corporation, New York, USA. The Ciba patent discloses a molecular sieve, which contains in all, or only in some of its cavities colourant molecules as well as a modifier which is covalently bound to said molecular sieve and which reduces its pore diameter. The patent further discloses a process for the preparation of the molecular sieve as well as the use of the molecular sieve as a pigment for colouring high molecular weight organic materials, preferably biopolymers and plastic materials, glasses, ceramic products for formulations of decorative cosmetics for the preparation of paint systems, preferably automotive lacquers, printing inks, dispersion paints and colour filters as well as materials comprising the novel molecular sieve.
U.S. Pat. No. 5,573,585 is assigned to Wolfgang Hoelderich of Germany. The Wolfgang patent discloses crystalline molecular sieves useful as a colourant which contain one or more chromophores of the class of mono- or -polyazo dyes that are devoid of acidic groups.
International patent application publication number WO 02/36940 is assigned to the University of Bern, Switzerland. The University of Bern publication discloses a dye loaded zeolite material comprising: a) at least one zeolite crystal having straight through uniform channels each having a channel axis parallel to, and a channel width transverse to, a c-axis of crystal unit cells; b) closure molecules having an elongated shape and consisting of a head moiety and a tail moiety, the tail moiety having a longitudinal extension of more than a dimension of the crystal unit cells along the c-axis and the head moiety having a lateral extension that is larger than said channel width and will prevent said head moiety from penetrating into a channel; c) a channel being terminated, in generally plug-like manner, at least at one end thereof located at a surface of the zeolite crystal by a closure molecule hose tail moiety penetrates into said channel and whose head moiety substantially occludes said channel end while projecting over said surface; and d) an essentially linear arrangement of luminescent dye molecules enclosed within a terminated channel adjacent to at least one closure molecule and exhibiting properties related to supramolecular organisation.
A paper by Calzaferri et al. in the Journal Microporous and Mesoporous Materials, Volume 95 (2006), pages 112-117, is titled “Carboxyester functionalised dye-zeolite L host-guest materials”. The publication discloses a method for the selective modification of zeolite L channel ends with carboxyl terminated groups. The success of the method is tested by vibrational spectroscopy, optical microscopy and energy transfer experiments after binding strongly luminescent dyes to the carboxyl groups. The method was carried out on 5000 nm and 30 nm sized zeolite L crystals.
A further paper by Calzaferri et al. in the Journal Microporous and Mesoporous Materials, Volume 90 (2006), pages 69-72, is titled “Solubilisation of dye-loaded zeolite L nanocrystals”. The publication discloses a method for the solubilisation of zeolite L nanocrystals in different solvents by grafting alkoxysilane derivatives with a hydrophobic part to the zeolite nanocrystal, which leads to a transparent suspension in non-polar solvents, while modification with a positively charged complex leads to solubilisation in water.
A further paper by Calzaferri et al. in the Journal Microporous and Mesoporous Materials, Volume 72 2004, pages 1-23, is titled “Molecular sieves as host guest materials for supramolecular organisation”. The publication discloses the use of zeolites and mespoporous silicas as host materials for the supramolecular organisation of organic dye molecules.
With the aim of developing a device system that exploits intermolecular excitonic interactions in one dimensional geometries, the present invention discloses the use of advanced single crystal fluorescence lifetime and spectrally resolved confocal microscopic methods to manufacture and investigate examples of J-aggregate coupling between chromophores (florescent dye molecules) in the sub nano-metre, one-dimensional nano-channels of zeolite L crystals.
Pyronine, DXP, PDI and oxonine intercalated with zeolite L have been used for the study of the unidirectional energy transfer as well as applications in highly fluorescent self assembling micro objects.
A prior art document CHEMPHYSCHEM 2003, Volume 4, pages 567-587, and describes electronic exitation energy migration in a photonic dye-zeolite, where Forster-type materials have been observed. Electronic excitation energy migration in a photonic host-guest material has been investigated by time resolved experiments and by Monte Carlo calculations. The host consists of a linear channel system (zeolite L crystal). The linear channels are filled with energy transporting dyes (donors) in their middle section and by one or several monolayers of a strongly luminescent trapping dye (acceptors) at each end of the linear channels. Excitation energy is transported among the donors in a series of steps until it reaches an acceptor at one of the channel ends, or it is somehow trapped on its way, or escapes by spontaneous emission. The organisation of chromophores in the linear channels is reported by Monte Carlo simulation and reports time resolved on a variety of pyronine-zeolite L crystal, oxonine-zeolite L crystal, and oxinine, pyronine-zeolite L crystal materials. In the oxinine, pyronine-zeolite L crystal material, the pyronine acts as a donor and the oxinine as an acceptor. The CHEMPHYSCHEM 2003, 4, 567-587 document discloses that the luminescent decay of the crystals containing one kind of dye is a single exponential decay for moderate loading of the chromophore when measured under oxygen free conditions. However bi-exponential decay otherwise. The excitation energy is transported along the channels by a Forster type mechanism, where the excitation energy is emitted as a red luminescence.
The present invention describes the preparation of materials of one dimensional excitonic character of tuneable coherence length on the range of 30 nm to 10000 nm or 20 chromophores up to 70000 chromophores where J-aggregation is observed.
The coherence length is very important as it determines the range over which excitation can be transported without negligible loss of excitions.
In the prior art it is generally very difficult to control coherence length due to defects—and it is generally more difficult to have the coherence length in one dimension.
Arrays with very little distortions and defects can be made inside the one dimensional channels of the zeolites because the entropy that leads to the defects can be overcome by the enthalpy due to the size restrictions.
Length of the lifetime studies on the pyronine intercalated zeolite L crystal show loading dependent multi-exponential decays.
With the ultimate aims of developing a device system that exploits intermolecular excitonic interactions in one dimensional geometries, the present invention discloses the use of advanced single crystal fluorescence lifetime and spectrally resolved confocal microscopy methods to present a novel example of J-aggregate coupling between chromophore molecules in the sub nano-metre, one dimensional nano-channels of the zeolite L crystals.